This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. GPCRs are membrane proteins expressed in virtually all human tissues, and transmit a wide variety of signals in response to diverse stimuli (including light, hormones, injury, and inflammation). These signals regulate a diverse set of cellular responses via interaction with GTP-binding proteins. Many acute and chronic disease states are linked to GPCR function or malfunction, and 40-60% of commercially available drugs interact with a GPCR, making them targets for nearly 30% of drug discovery efforts worldwide. Together these drugs had an $84 billion market in 1995. Thus far over 300 GPCRs have been isolated, and the functions of about 150 are known. It is estimated that ~2000 GPCRs exist in the human genome. Efforts to understand GPCR function, structure, stability, and assembly are hampered by the difficulties associated with producing these integral membrane proteins. The goals of this COBRE mini-project are: 1) to establish the conditions for preparing isotopically enriched human A2a and human NK1 receptors in their functionally competent forms, and suitable for structural analysis by NMR spectroscopy, and 2) to acquire preliminary multidimensional solution or solid-state NMR spectra of the above receptors, for subsequent structural analysis. The long term goal of these efforts is to gain atomic-level structural information of these receptors. This project will accelerate the structural studies of the GPCR family of membrane proteins and enable an improved understanding of the ligand discrimination of this fascinating class of proteins.